实现range类

KeyError · 发表于 2023-1-17 17:17:31

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本帖最后由 KeyError 于 2023-1-17 17:18 编辑

>>> #shell
>>> help(range)
Help on class range in module builtins:
class range(object)
| range(stop) -> range object
| range(start, stop[, step]) -> range object
|
| Return an object that produces a sequence of integers from start (inclusive)
| to stop (exclusive) by step. range(i, j) produces i, i+1, i+2, ..., j-1.
| start defaults to 0, and stop is omitted! range(4) produces 0, 1, 2, 3.
| These are exactly the valid indices for a list of 4 elements.
| When step is given, it specifies the increment (or decrement).
|
| Methods defined here:
|
| __bool__(self, /)
| self != 0
|
| __contains__(self, key, /)
| Return key in self.
|
| __eq__(self, value, /)
| Return self==value.
|
| __ge__(self, value, /)
| Return self>=value.
|
| __getattribute__(self, name, /)
| Return getattr(self, name).
|
| __getitem__(self, key, /)
| Return self[key].
|
| __gt__(self, value, /)
| Return self>value.
|
| __hash__(self, /)
| Return hash(self).
|
| __iter__(self, /)
| Implement iter(self).
|
| __le__(self, value, /)
| Return self<=value.
|
| __len__(self, /)
| Return len(self).
|
| __lt__(self, value, /)
| Return self<value.
|
| __ne__(self, value, /)
| Return self!=value.
|
| __reduce__(...)
| Helper for pickle.
|
| __repr__(self, /)
| Return repr(self).
|
| __reversed__(...)
| Return a reverse iterator.
|
| count(...)
| rangeobject.count(value) -> integer -- return number of occurrences of value
|
| index(...)
| rangeobject.index(value) -> integer -- return index of value.
| Raise ValueError if the value is not present.
|
| ----------------------------------------------------------------------
| Static methods defined here:
|
| __new__(*args, **kwargs) from builtins.type
| Create and return a new object. See help(type) for accurate signature.
|
| ----------------------------------------------------------------------
| Data descriptors defined here:
|
| start
|
| step
|
| stop
>>>

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所以，我们今天来实现range类的基本功能

根据小甲鱼老师的生成器，代码显而易见

>>> class range:
def __init__(self, stop, /):
self.stop = stop
self.num = -1
def __iter__(self):
return self
def __next__(self):
self.num += 1
if self.num >= self.stop:
raise StopIteration
return self.num
>>>

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但是这样并不能传入开始值和步长

问题是如果只有一个参数，它应该是结束值，但有两个及以上，应该按开始值，结束值，步长的顺序传入。

两千年后，我终于想到了办法！

class range:
def __init__(self, *args, /):
if len(args) == 1:
self.stop = args[0]
self.num = -1
self.add = 1
elif len(args) == 2:
self.stop = args[1]
self.num = args[0] - 1
self.add = 1
elif len(args) == 3:
self.stop = args[1]
self.num = args[0] - 1
self.add = args[2]
elif len(args) == 0:
raise TypeError("range expected at 1 argument, got 0")
else:
raise TypeError(f"range expexct ed at 3 argument, got {len(args)}")
def __iter__(self):
return self
def __next__(self):
self.num += self.add
if self.num >= self.stop:
raise StopIteration
return self.num
>>>

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>>> for i in range(1, 10, 2):
print(i)
1
3
5
7
9
>>>

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完美！

match123_xbd · 发表于 2023-4-8 15:38:03

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